Liquefaction mechanism of lignin in the presence of phenol at elevated temperature without catalysts - Studies on beta-O-4 lignin model compound .2. Reaction pathway
Liquefaction mechanism of lignin in the presence of phenol at elevated temperature without catalysts - Studies on beta-O-4 lignin model compound .2. Reaction pathway
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DOI：
10.1515/hfsg.1997.51.4.325
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发表时间：
1997-01-01
期刊：
影响因子：
2.4
通讯作者：
Shiraishi, N
中科院分区：
文献类型：
--
作者：
Lin, LZ;Yoshioka, M;Shiraishi, N
以愈创木酰基甘油-β-愈创木基醚（GG）为起始材料，研究木质素在苯酚存在下高温下的液化机理。基于反应中间体的结构及其形成和转化动力学，提出了GG的自由基反应途径，并通过一系列相应的模型反应进一步证实。也就是说，GG首先在其β-O-4键上进行均裂，产生松柏醇和愈创木酚自由基作为主要的基本中间体。松柏醇自由基在其侧链上由共轭双键组成，主要与苯酚自由基发生广泛反应，产生一系列相应的酚化产物。该反应途径主导了整个动态液化过程，并导致了反应产物的多样性。相比之下，愈创木酚自由基大部分被还原为愈创木酚，其中一些与苯酚自由基反应，得到相应的二聚偶联产物。这些二聚偶联化合物相当稳定，并且在最终聚合产物的形成中发挥次要作用。
Guaiacylglycerol-beta-guaiacyl ether (GG) was used as a starting material to study the liquefaction mechanism of lignin in the presence of phenol under elevated temperature. Based on the structures of the reaction intermediates and their formation and conversion kinetics, a radical reaction pathway for GG is proposed, which was further confirmed by a series of corresponding model reactions. That is, GG first underwent homolytic cleavage at its beta-O-4 linkage to yield coniferyl alcohol and guaiacol radicals as the major elementary intermediates. The coniferyl alcohol radical, which consists of a conjugated double bond in its side chain, reacted extensively, mainly with a phenol radical to yield a series of corresponding phenolated products. This reaction pathway dominated the whole dynamic liquefaction process and contributed to the multiplicity to the reaction products. By contrast, the guaiacol radical was mostly reduced to guaiacol and some of it reacted with the phenol radical to afford the corresponding dimeric coupling products. These dimeric coupling compounds were rather stable and played minor roles in the formation of the final polymeric products.